[Plasma cortisol concentrations and circadian rhythm in healthy young Japanese and caucasians (author's transl)].

We report herein a method of solid-phase radioimmunoassay (RIA) for assessment of plasma cortisol concentration using 125I-labeled ligand [CORTCTK-125]. Plasma cortisol concentrations and its circadian rhythm in healthy young Japanese and American whie women were also evaluated using CORTCTK-125. Nineteen Japanese women, of an average age of 20.3 +/- 0.1 years, and 12 Caucasians of mixed ethnic origin (Minnesota), average 20.0 +/- 0.5 years, were studied using a similar protocol. The distribution of the menstrual stage of the two groups was similar. Blood was drawn from each subject into EDTA containers at 4-hour intervals starting at 0800 on one day and was continued for the ensuing 24 hours. The samples were immediately placed in a refrigerated centrifuge at 4 degrees C, and then stored at -20 degrees C until the assay. The samples from Minnesota were packed in dry ice and brought by air to Japan. Determinations of plasma cortisol concentration in samples from both groups were carried out at Kyushu University. Advantages of the solid-phase RIA method are as follows: (1) 0.05 ml of plasma or serum was sufficient for determination of plasma cortisol concentrations, (2) no other solvents or solutions for the extraction or purification were required, (3) the procedure was simple and readily facilitated, and (4) the concentration of cortisol in heparin-plasma was somewhat higher than that in serum or EDTA-plasma, but there was no statistical difference. Plasma cortisol concentrations in the samples from the Japanese (19.73 +/- 1.44 on the first and 18.94 +/- 1.32 microgram/dl on the second day) and that of the American group (17.48 +/- 2.38 and 19.37 +/- 2.16 microgram/dl, respectively) at 0800 was similar. The average value of 7 determinations at 4-hour intervals was 11.01 +/- 2.00 microgram/dl in the Japanese and 10.29 +/- 1.05 microgram/dl in the American group. A remarkable and similar circadian rhythm was observed in both groups with a peak at 0800 and with nadirs at 2000 in the Japanese (4.80 +/- 0.45 microgram/dl) and 2400 in the American group (5.18 +/- 0.83 microgram/dl). There were statistically significant differences between the values at the peak and the nadir. The related subjects were then classified into Group-F (9 subjects) and Group-T (9); the former included high body mass index [BMI: body weight(kg)/body height(m)2] of more than 24.0, and the latter included a relatively lower BMI of less than 21.5. The circadian rhythm of both groups revealed a similar pattern, whereas plasma cortisol concentration was always higher in Group-F than in Group-T, at all 7 determinations. There were no significant differences except for the value at 0400. Furthermore, the average values of plasma cortisol concentration and circadian rhythm were compared; the group with a larger body surface area (BSA) (Group-L) and the group with a smaller BSA (Group-S). No difference was found in the plasma cortisol concentration of Group-L and -S, and the circadian rhythm was similar in both groups...